1. Field of the Invention:
The invention in general relates to the drilling of oil or gas wells, and particularly to the acoustic detection of a kick.
2. Description of the Prior Art:
In the drilling of an oil or gas well, drilling fluid referred to in the industry as "mud", is pumped into the drill pipe where it proceeds out through the drill bit and up the annular space between the drill pipe and the walls of the hole and further up the annular space between the drill pipe and the casing generally used, after which it is examined at the surface for certain parameters, processed and returned to circulation. The purpose of the circulating mud is to clean, cool and lubricate the bit, flush to the surface the cuttings from the bore hole and to protect the walls of the hole until casing is inserted. The density of the mud is carefully controlled at the surface so as to contain various pressures encountered in the hole.
As the well is drilled, gases or high pressure fluids may be released from porous rock and find their way into the circulating mud. This may result in a modification of the buoyancy of the drilling string and can cause extensive damage if it goes undetected. This gas or liquid influx reduces the hydrostatic head in the annulus and is known as a kick. If the volume of the kick is not excessive and if it can be detected, procedures may be instituted so that drilling operations may proceed with minimal disruption.
An uncontrolled kick is called a blowout, which have been known to cause extensive equipment damage, fires, and possible release of noxious gases. Accordingly, some means of detecting the initial kick is desired.
The present invention provides such need and utilizes acoustic methods.
Acoustic methods have been utilized for years in the oil and gas well production area. For example, after the completion of a well, the depth of fluid standing in the well is desired to be known because such information is helpful in proper setting and operation of pumps used in the wells. In order to determine the height of the standing fluid in the well, many systems transmit an acoustic pulse from the top of the casing, in the annular spacing between the casing and the tubing. The sound pulse travels down the well and is reflected back up from the fluid-air interface to provide an indication of fluid level.
During the drilling of some wells, apparatus is utilized which transmits acoustic signals down the drill pipe itself for telemetry and control purposes.
Schemes for acoustically monitoring for kicks include the examination at the surface of the circulating mud by acoustically monitoring mud flow rates or by examining acoustic attenuation of signals propagated through the mud.
In yet another detector, an acoustic transmitter of low frequency is placed on the casing, or the like, to laterally displace any bubbles which might be contained in the circulating mud. A higher frequency Doppler detection system is then operable to detect the relatively displaced bubbles.
The present invention provides a relatively simple means providing an early indication of a kick to permit immediate action to be taken to prevent catastrophic results or to achieve quick return to normal drilling operations. Further, the apparatus may also provide a record of drilling rate.